Unimolocular Micelles Containing Metal Nanoparticles and their Use as Catalyst for Synthesis of Carbon-Carbon-Bonds

ABSTRACT

Disclosed are metal nanoparticle containing unimolecular micelles comprising selected star-shaped block-copolymers. These unimolecular micelles can be used as catalysts in coupling reactions forming carbon-carbon-bonds, for example as catalysts in the Heck reaction.

This invention relates to metal nanoparticle containing unimolecularmicelles comprising selected block-copolymers. These unimolecularmicelles can be used as catalysts in coupling reactions formingcarbon-carbon-bonds.

BACKGROUND OF THE INVENTION

The use of metal nanoparticles as catalysts for carbon-carbon-bondformation is known. Various methods for preparation and stabilization ofmetal nanoparticles are described.

Chem. Mater. 2000, 12, 22-4 discloses catalytic Pd nanoparticlessynthesized using a lyotropic liquid crystal polymer template. Pdnanoparticles with small diameters are formed in a polymer matrix whichcan be used as catalyst for Heck reaction.

JACS 2005, 127, 2125-35 discloses formation of nanoarchitecturesincluding subnanometer Pd clusters and their use as highly activecatalysts. The stabilization of clusters in several micellemorphologies, i.e. in spherical micelles and in non-spherical micelles,is described. The micelles are produced from functional polystyrenecopolymer and can be used as catalyst for Heck reaction. This documentdoes not disclose the preparation of unimolecular micelles.

In Nano Letters 2001, vol. 1 (1), 14-17 the Heck heterocoupling with adendritic nanoreactor is described wherein Pd nanoclusters are prepared.These nanoclusters are encapsulated in PPI dendrimers. These polymers donot possess a core-shell architecture.

In JACS 1997, 119, 10116-20 the preparation of Pd colloids in blockcopolymer micelles is disclosed. These colloids are used for thecatalysis of the Heck reaction. The Pd clusters are encapsulated inmicelles of functionalized polystyrene. This document does not disclosepreparation and use of unimolecular micelles.

Langmuir 2005, 21, 2408-2413 describes keggin ion mediated synthesis ofhydrophobized Pd nanoparticles for multifunctional catalysis. Pdclusters are prepared which are encapsulated in octadecylamine. Theseare used as catalyst for Heck reaction in a hydrocarbon solvent. Pdclusters stabilized in unimolecular micelles are not disclosed.

JACS 2002, 124, 14127-14136 describes layered double hydroxide supportednanopalladium catalyst for Heck-, Suzuki-, Sosnogashira- and Stille-typecoupling reactions of chlororarenes. Pd nanoparticles supported on LDHare disclosed. The Pd nanoparticles are not encapsulated in anunimolecular micelle.

In Journ. Of Molecular Catalysis A: Chemical 229 (2005), 7-12 thepreparation of Pd nanoparticles in polyethylene glycol is disclosed.These can be used as efficient and recyclable catalysts for Heckreaction. The Pd clusters are stabilized in a polyethylene glycolmatrix. This document does not disclose Pd clusters encapsulated inunimolecular micelles.

Langmuir 2003, 19, 7682-7684 describes PAMAM-dendrimer stabilized Pdnanoparticles as a catalyst for the Suzuki reaction. For thestabilization of the Pd nanoparticles dendrimers are applied and nopolymers with core-shell architecture.

In Adv. Funct. Mater. 2004, 14 (10), 999-1004 the shape-selectivesynthesis of Pd nanoparticles stabilized by highly branched amphiphilicpolymers is disclosed. The polymers used possess a core-shell structurebut they are not defined.

Nano Letters 2003, vol. 3 (12), 1757-1760 describes synthesis,characterization and catalytic applications of a Pd-nanoparticle coreddendrimers. The Pd nanoparticles can be used as catalysts for the Heckreaction. But no unimolecular micelles are disclosed and the polymersare dendrimers possessing no core-shell structure.

Thus, from the prior art Pd nano particles with small diameters arealready known as catalysts for the formation of carbon-carbon-bonds.However, the small particles are not based on the stabilization withstar-shaped block copolymer structures.

Unimolecular micelles made from dendrimers are also known.

U.S. Pat. No. 5,154,853 discloses unimolecular micelles made fromdendrimers consisting essentially of alkyl or alkylene groups and theirpreparation. The dendrimers do not possess a core-shell structure. Nostabilization of nanoparticles is disclosed.

U.S. Pat. No. 5,376,690 and U.S. Pat. No. 5,516,810 disclosemetallospheres and superclusters which are prepared from unimolecularmicelles containing internal void areas with reactive sites capable ofcovalent and noncovalent bonding to metal and non-metal guests. Thedendrimers forming the unimolecular micelles do not possess a core-shellstructure.

From WO-A-96/03,114 and WO-A-98/08,491 lock and key unimolecularmicelles are known. These include at least one engineered acceptorspecifically binding a ligand. A key unimolecular micelle comprises acore molecule and a plurality of branches extending therefrom. At leastone of the branches includes a shank portion extending therefrom havinga terminal moiety at an end thereof for binding to a complementaryacceptor of a lock unimolecular micelle. Lock and key micelles togetherform an unit. Unimolecular micelles with core-shell structures are notdisclosed.

Star-shaped block copolymers are also disclosed in the prior art.

EP-A-156,079 discloses star-shaped polyether polyoxyethylene prepolymersand star-shaped block copolymers made therefrom. The end products arecharacterised by high impact resistance and high heat resistance and beused as molding resins, i.e. for the production of fibres or foams.

WO-A-03/78,489 discloses amphiphilic block copolymers, for examplestar-block copolymers. These comprise a biodegradable polymer covalentlyattached at the polymer ends to at least one hydrophilic vinyl polymervia a divalent sulfur atom. The block copolymers are used in therapeuticcompositions.

WO-A-00/59,968 discloses a process for preparing graft-block copolymerswhich can possess a star-shape.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a catalyst forcarbon-carbon-bond formation which is cheaper and easy to synthesize.

Another object of the present invention is the provision of a highlyefficient catalyst for carbon-carbon-bond formation which can be used insmaller amounts to obtain the same conversion as compared with knowncatalysts for these reactions.

Still another object of the present invention is the provision of acatalyst for carbon-carbon-bond formation which is based onbiocompatible polymers and might be used for the synthesis of compoundsapplied in biological material without adversely affecting this.

Surprisingly it has been found that in unimolecular micelles of selectedblock-copolymers metal nanoparticles can be formed which are highlyactive catalysts for carbon-carbon-coupling reactions, such as Heckreaction, Suzuki-reaction, Sosnogashira-reaction and Stille-reaction.

The catalysts of this invention are made from materials which arecheaper and easier to synthesize as the materials used in the prior artand which provide at least the same results than other smallmetal-nanoparticle containing materials.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an unimolecular micelle comprisingmetal nanoparticles and a star-shaped block copolymer containing atleast one hydrophilic block that is prepared from monomers which resultin hydrophilic polymers, preferably a hydrophilic block selected fromthe group consisting of polyether block, poly-N-vinyl-heterocyclic blockand polyacrylic and/or polymethacrylic block comprising hydroxyl, amino,amido and/or carboxyl groups and at least one hydrophobic block that isprepared from monomers which result in hydrophobic polymers, preferablya hydrophobic block selected from the group consisting of polyesterblock, polyolefin block, polyacrylate and/or polymethacrylate block andpolyurethane block.

The term “unimolecular” micelle as used in this specification shall meana functional unit made from one polymer molecule being dispersed in asolvent or in a molten material, said polymer molecule bearing acore-shell architecture and therefore provide micellar properties, e.g.a different solubility of the core than the shell, without the necessaryself assembly step of classical micelles. These unimolecular micelleswill have a micellar structure and behavior in different solvents unlikeclassical micelles. The unimolecular micelles of this invention can beof different shape, for example of spherical, elliptical, cylindrical,lamellar or worm-like shape. In case of rotation symmetry a particlediameter can be determined. Typical average diameters are in the rangeof 1-200 nm, preferably 1-50 nm and very preferred 1-20 nm (determinedvia dynamic light scattering).

Star-shaped block copolymers which are used for the unimolecularmicelles of this invention are polymers possessing a star-likearchitecture. These molecules possess a central branching portion,providing at least three branches of block copolymer units.

The star-shaped block copolymers which can be used in this inventionhave a structure of the general formula I or II

R¹-[(hydrophilic block)-b-(hydrophobic block)-R²]_(z)  (I)

R¹-[(hydrophobic block)-b-(hydrophilic block)-(b-hydrophobicblock)_(y)-R²]_(z)  (II)

whereinz is an integer of at least 3, preferably between 3 and 32 and verypreferably between 3 and 8,y is 0 or 1,R¹ is a z-valent organic group,R² is hydrogen, hydroxyl or an organic group, preferably hydrogen or analkyl or aryl group,hydrophilic block is a block that is prepared from monomers which resultin hydrophilic polymers, preferably a polyether block, apoly-N-vinyl-heterocyclic block or a polyacrylic and/or polymethacrylicblock comprising hydroxyl, amino, amido and/or carboxyl groups,hydrophobic block is a block that is prepared from monomers which resultin hydrophobic polymers, preferably a polyester block, a polyolefinblock, a polyacrylate and/or polymethacrylate block and/or apolyurethane block, andb is a two-valent to penta-valent linker, preferably a two-valentlinker, between the hydrophilic group and the hydrophobic group,preferably a covalent bond, a bivalent hydrocarbon group, an estergroup, an ether group or an amide group.

Structures of formula I are preferred.

The hydrophilic blocks are prepared from monomers which result inhydrophilic polymers. These hydrophilic polymers can be derived from oneor more monomers. (homopolymer blocks or copolymer blocks). The term“hydrophilic” as used in this description means a homo- or copolymerwith a water solubility of the hydrophilic blocks of at least 100 g/L,preferably at least 200 g/L, especially preferred 300 g/L at 25° C.

The hydrophobic blocks are prepared from monomers which result inhydrophobic polymers. These hydrophobic polymers can be derived from oneor more monomers. (homopolymer blocks or copolymer blocks). The term“hydrophobic” as used in this description means a homo- or copolymerwith a water solubility of the hydrophobic blocks of less than 100 g/L,preferably less than 50 g/L, especially preferred less than 25 g/L at25° C.

Preferably the hydrophilic blocks are polyether blocks, very preferablypolyalkylene glycol blocks, especially preferred polyethylene glycolblocks.

Other preferred hydrophilic blocks are derived from N-vinyl-heterocycliccompounds, such as N-vinylpyridine, N-vinylpyrrolidone orN-vinylimidazole.

Other preferred hydrophilic blocks are derived from acrylic acid and/ormethacrylic acid and/or their hydrophilic modified esters or amidescarrying hydroxyl, amino, amido and/or carboxyl groups which blocksoptionally contain co-units derived from vinylpyridine comonomers.Examples of these monomers are acrylic acid, methacrylic acid,hydroxyethylmethacrylic acid, acrylamide or methacrylamide.

Preferably the hydrophobic blocks are polyester blocks, preferablyderived from aliphatic and/or aromatic dicarboxylic acids and aliphaticalcohols or from lactones, preferably from caprolactone.

Other preferred hydrophobic blocks are derived from ethylenicallyunsaturated hydrocarbons, such as from alpha-olefins, for example fromethylene or propylene, or from vinylaromatic compounds, such as styrene.

Other preferred hydrophobic blocks are derived from acrylic estersand/or methacrylic esters, preferably from alkylacrylates and/oralkylmethacrylates or their cycloalkyl derivatives, such asbutylacrylate, methylmethacrylate, hexylacrylate,cyclohexyl(meth)acrylate or isobornyl(meth)acrylate.

Still other preferred hydrophobic blocks are derived from diisocyanatesand diols to form polyurethane blocks, preferably from aliphatic oraromatic diisocyanates and aliphatic diols.

The hydrophilic blocks and/or hydrophobic blocks can be made fromhomopolymers or from copolymers.

Preferred star-shaped block copolymers which can be used in thisinvention have a structure of the general formula III or IV

R¹-[((PE)-b-(PES))_(x)—R²]_(z)  (III)

R¹-[((PES)-b-(PE))_(x)-(b-PES)_(y)-R²]_(z)  (IV)

whereinPE is a polyether block, preferably with 2-100 recurring polyetherunits, very preferably 2-30 recurring polyether units,PES is a polyester block, preferably with 1-100 recurring polyesterunits, very preferably 2-30 recurring polyester units,x is an integer of at least 1, preferably between 1 and 30,y is 0 or 1, andR¹, R², b and z are as defined above.

Examples of polyether blocks are recurring units of formula V

(—O—R³)_(a)—  (V)

wherein a is an integer of at least 2, very preferably from 2 to 30, andR³ is an alkylene, cycloalkylene, arylene or aralkylene-group,preferably an alkylene group possessing two to six carbon atoms.

The PE block may be linked via its oxygen atom or a carbon atom to thegroup R¹. Different linking groups can be present between R¹ and PE.Examples thereof are covalent bonds, ether groups or ester groups.

Examples of polyester blocks are recurring units of formula VIa or VIb

(—R⁴—COO)_(b)—  (VIa)

(—R⁵—COO—R⁶—COO)_(c)—  (VIb)

wherein b and c independently of one another are integers of at least 1,very preferably from 2 to 30,R⁴, R⁵ and R⁶ independently of one another are alkylene, cycloalkylene,arylene or aralkylene-groups, preferably an alkylene groups possessingtwo to six carbon atoms.

The PES group may be linked via its oxygen atom or a carbon atom to thegroup R¹. Different linking groups can be present between R¹ and PES.Examples thereof are covalent bonds, amine groups, ester groups or amidegroups.

Preferred groups R¹ are derived from trimethylolpropane, glycerol,pentaerythrite, dipentaerythrite, carbohydrates, such as glucore,mannose or fructose, or sorbitol, trimesic acid,ethylenediaminetetraacetic acid and diamino-polyalkyleneimines,preferably H₂N—CH₂—CH₂—NH—CH₂—CH₂—NH₂.

The star-shaped block copolymers used to form the unimolecular micellesof this invention can be prepared by methods known to those skilled inthe art. Their synthesis is, for example, disclosed in JACS 2004, 126,p. 11517-21.

The unimolecular micelles of this invention stabilize metalnanoparticles which can be obtained by adding to a solution containingthe unimolecular micelles a solution of a metal salt. The metal salt isincorporated into the core of the unimolecular micelles by adding saidsalt to the liquid containing said unimolecular micelles and the metalsalt is subsequently reduced to form stabilized metal nanoparticleswithin the unimolecular micelle.

As solvents for forming the unimolecular micelles to be used in thisinvention organic solvents, for example benzene, toluene, chlorotolueneor chloroform can be used. Preferably polar, aprotic organic solventsare used, for example dimethylsulfoxide, dimethylformamide ordimethylacetamide.

In general each metal including metal alloys (hereinafter togethercalled “metals”) can be chosen for incorporation into the unimolecularmicelles of this invention. Non limiting examples are metals of groupsIB-VIIIB of the Periodic Table of Elements, preferably metals of thegroup IB and VIIIB of the Periodic Table of Elements. Preferablyplatinum, palladium, gold, silver, nickel or iron are used. Mixtures ofdifferent metals can also be used.

The metals are present as nanoparticles within the core (=the centralportion) of the unimolecular micelles. Typical mean particle diametersof the metal nanoparticles are in a range between 1 nm and 100 nm,preferably 1 nm-10 nm, very preferably between 1 and 5 nm. The meanparticle diameter is determined via TEM measurements.

Very preferably metal nanoparticles are incorporated into theunimolecular micelle of this invention, which catalyse the formation ofcovalent carbon-carbon bonds. A typical example of such a reaction isthe Heck reaction.

A specific feature of the metal nanoparticles used in this invention forcatalysis is their high surface to volume ratio. This feature isregarded to promote the catalytic action as it is believed that thereaction is taking place on the metal surface of the particles.

The incorporation of metal nanoparticles into the unimolecular micellesof this invention can be obtained by treating a unimolecular micellecontaining solution with the solution of a metal salt of the metal to bedeposited within the unimolecular micelles. After this treatment themetal is generated by reduction of the metal salt.

Typical examples of metal salts are acetates or chlorides, such aspalladium acetate or palladium chloride. Typical examples of reducingagents are NaBH₄, LiAlH₄ or NaAlH₄.

This invention also relates to the use of the metal nanoparticlesstabilized within unimolecular micelles as catalysts in a reaction forthe formation of covalent carbon-carbon bonds.

The following Examples illustrate the invention without any limitation.

EXAMPLES

5-arm star-shaped block copolymers of the following structure wereprepared

R¹²—[(R¹³—O)_(l)—(OC—R¹⁴—O)_(j)]_(k)—R¹⁵,

whereinR¹² is a pentavalent group derived from H₂N—CH₂—CH₂—NH—CH₂—CH₂—NH₂,R¹³ is ethylene,R¹⁴ is pentamethylene,R¹⁵ hydrogen,k is 5,l has an average value of 9, andj has an average value between 1 and 18.

These 5-arm star-shaped block copolymers were used to stabilizepalladium nanoparticles in the following way:

The poly(ethylene glycol) core was swelled with palladium acetate(Pd(CH₃COO)₂) in N,N-dimethylformamide (DMF) for 24 hours andwell-defined Pd nanoparticles (about 3 nm diameter as determined by TEM(transmission electron microscopy)) were further obtained afterreduction with NaBH₄. These nanoparticles were utilized for HeckC—C-coupling reactions between 4-bromo-acetophenone and styrene to form1-[4-((E)-Styryl)-phenyl]-ethanone in high yields with low catalystloadings. More specifically, palladium nanoparticles stabilized by blockcopolymers with R¹² being a pentavalent group derived fromN*1*-(2-Aminoethyl)-ethane-1,2-diamine, R¹³ being ethylene, R¹⁴ beingpentamethylene, R¹⁵ being hydrogen, k being 5, l having an average valueof 9, and j having an average value between 0 and 18, and possessing apalladium loading of 1 Pd per 4 ethylene oxide repeat units applying a2-fold excess of NaBH₄ according to Pd for the reduction all provided100% conversion for the above mentioned reaction within 24 hoursreaction time at 100° C. in N—N-dimethylformamide as the solvent with aPd content of 0.1 mol %.

1. An unimolecular micelle comprising metal nanoparticles and astar-shaped block copolymer containing at least one hydrophilic blockthat is prepared from monomers which result in hydrophilic polymers andat least one hydrophobic block that is prepared from monomers whichresult in hydrophobic polymers.
 2. An unimolecular micelle according toclaim 1, wherein the hydrophilic block is selected from the groupconsisting of polyether block, poly-N-vinyl-heterocyclic block andpolyacrylic and/or polymethacrylic block comprising hydroxyl, amino,amido and/or carboxyl groups and wherein the hydrophobic block isselected from the group consisting of polyester block, polyolefin block,polyacrylate and/or polymethacrylate block and polyurethane block.
 3. Anunimolecular micelle according to claim 1, wherein the star-shaped blockcopolymers have a structure of the general formula I or IIR¹-[(hydrophilic block)-b-(hydrophobic block)-R²]_(z)  (I)R¹-[(hydrophobic block)-b-(hydrophilic block)-(b-hydrophobicblock)_(y)-R²]_(z)  (II) wherein z is an integer of at least 3, y is 0or 1, R¹ is a z-valent organic group, R² is hydrogen, hydroxyl or anorganic group, preferably hydrogen or an alkyl or aryl group,hydrophilic block is a block that is prepared from monomers which resultin hydrophilic polymers, preferably a polyether block, apoly-N-vinyl-heterocyclic block or a polyacrylic and/or polymethacrylicblock comprising hydroxyl, amino, amido and/or carboxyl groups,hydrophobic block is a block that is prepared from monomers which resultin hydrophobic polymers, preferably a polyester block, a polyolefinblock, a polyacrylate and/or polymethacrylate block and/or apolyurethane block, and b is a two-valent to penta-valent linker betweenthe hydrophilic group and the hydrophobic group, preferably a covalentbond, a bivalent hydrocarbon group, an ester group, an ether group or anamide group.
 4. An unimolecular micelle according to claim 3, whereinthe star-shaped block copolymers have a structure of the general formulaIII or IVR¹-[((PE)-b-(PES))_(x)-R²]_(z)  (III)R¹-[((PES)-b-(PE))_(x)-(b-PES)_(y)-R²]_(z)  (IV) wherein PE is apolyether block, PES is a polyester block, x is an integer of at least1, y is 0 or 1, and R¹, R², b and z are as defined in claim
 3. 5. Anunimolecular micelle according to claim 4, wherein the polyether blocksare recurring units of formula V(—O—R³)_(a)—  (V) wherein a is an integer of at least 2, preferably from2 to 30, and R³ is an alkylene, cycloalkylene, arylene oraralkylene-group, preferably an alkylene group possessing two to sixcarbon atoms.
 6. An unimolecular micelle according to claim 4, whereinthe polyester blocks are recurring units of formula VIa or VIb(—R⁴—COO)_(b)—  (VIa)(—R⁵—COO—R⁶—COO)_(c)—  (VIb) wherein b and c independently of oneanother are integers of at least 1, and R⁴, R⁵ and R⁶ independently ofone another are alkylene, cycloalkylene, arylene or aralkylene-groups,preferably an alkylene groups possessing two to six carbon atoms.
 7. Anunimolecular micelle according to claim 3, wherein the groups R¹ arederived from trimethylolpropane, glycerol, pentaerythrite,dipentaerythrite, carbohydrates, sorbitol, trimesic acid,ethylenediaminetetraacetic acid and diamino-polyalkyleneimines.
 8. Anunimolecular micelle according to claim 7, wherein the groups R¹ arederived, from H₂N—CH₂—CH₂—NH—CH₂—CH₂—NH₂.
 9. An unimolecular micelleaccording to claim 1, wherein the metal is a metal of groups IB-VIIIB ofthe Periodic Table of Elements, preferably a metal of the group IB andVIIIB of the Periodic Table of Elements or mixtures thereof.
 10. Anunimolecular micelle according to claim 8, wherein the metal isplatinum, palladium, gold, silver, nickel or iron.
 11. An unimolecularmicelle according to claim 1, wherein the metal nanoparticles possessmean particle diameters in a range between 1 nm and 100 nm, preferably 1nm-10 nm, very preferably between 1 and 5 nm.
 12. Use of theunimolecular micelles according to claim 1 as catalysts in a reactionfor the formation of covalent carbon-carbon bonds.